Drive mechanism, particularly for a moveable part of a closing unit or the injection unit of a plastic injection moulding machine

ABSTRACT

A drive device has a drive element movable axially by means of an electric motor and a hydraulic unit. In the drive device it is important to execute a rapid adjusting movement and then to exert high forces. This causes high reaction forces on the lifting spindle. High reaction forces are avoided if a force intensifier with two pistons movable in relation to one another and differing from one another in the size of their active surfaces along with an intermediate part which, together with the pistons, encloses a pressure space filled with a pressure fluid is used, if the smaller active surface is connected mechanically to the drive element, for the adjusting movement, the hydraulic unit can be moved as a whole, and if, for exerting a high force by means of the larger active surface, the intermediate part can be blocked against displacement in relation to a fixed stand.

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a drive device which is provided, inparticular, for driving a movable part of the closing unit or of theinjection unit of a plastic injection molding machine.

Within the closing unit of a plastic injection molding machine, thedrive device moves the movable mold clamping plate of the machine. Sucha drive device must fulfill two important different requirements. On theone hand, it is to move the mold clamping plate as quickly as possiblein order to close and to open the mold, so that the cycle time forproducing a molding can be kept short. On the other hand, it is to becapable of keeping the mold clamping plate and consequently the entiremold shut with great force against the high injection pressure. On theone hand, therefore, adjusting movements are to be executed at highspeed and, on the other hand, high forces are to be exerted without anyappreciable movement. Requirements of this kind may arise not only withregard to the closing unit, but also in respect of the injection unit ofa plastic injection molding machine. For example, when plastic is beinginjected into the mold, the plasticizing worm is moved at relativelyhigh speed in the direction of the mold, until the mold is filledcompletely with plastic. When the plastic melt contained in the mold issubsequently exposed to what may be referred to as dwell pressure, thedrive has to apply a high force without any appreciable movement of theplasticizing worm.

U.S. Pat. No. 4,030,299 discloses a purely hydraulic drive for themovable mold clamping plate of a plastic injection molding machine, saiddrive also containing a hydraulic force intensifier. The latter has amovable piston with a small active surface, a further movable pistonwith a large active surface and a cylinder which, together with thepistons, encloses a pressure space filled with a pressure fluid. Thecylinder is arranged at a fixed location on the stand of the injectionmolding machine. The drive includes, moreover, hydraulic cylinders whichmove the movable mold clamping plate in order to close and open themold. When the mold is in the open state, the volume of the pressurespace of the hydraulic force intensifier is minimal. If, then, themovable mold clamping plate is moved by the hydraulic cylinders with theeffect of a closing of the mold, the large piston of the hydraulic forceintensifier is taken up, the volume of the pressure space of thehydraulic force intensifier increasing and pressure medium flowing outof a reservoir into the pressure space via a suction follow-up valve.Thereafter, the small piston of the hydraulic force intensifier is movedinto the pressure space, thereby generating a high pressure which bringsabout a high closing force via the large active surface of the largepiston. The small piston is moved hydraulically due to the supply ofpressure fluid. Thus, in the drive device according to U.S. Pat. No.4,030,299, various hydraulic drive components are present for theadjusting movement of the movable mold clamping plate and for exerting ahigh force. During the adjusting movements of the mold clamping plate, alarge amount of pressure fluid flows back and forth between the pressurespace and the reservoir, thus necessitating correspondingly large valvesand fluid ducts.

A drive device is known from DE 41 11 594 A1. In this drive device, ahydraulic cylinder having a large active surface is firmly connected tothe movable mold clamping plate. The unit consisting of the movable moldclamping plate and of the hydraulic cylinder can be moved by an electricmotor, via a mechanism comprising a lifting spindle and a spindle nut,in order to close the mold quickly and open it quickly. The high closingforce is applied by the action of pressure upon the hydraulic cylindermovable together with the mold clamping plate. In this case, the entirereaction force is diverted to the machine stand via the spindle and thespindle nut. The spindle must therefore have a highly robust design, isoverdimensioned for the adjusting movement and is correspondinglycostly.

SUMMARY OF THE INVENTION

The object on which the invention is based is to develop further a drivedevice such that, at low outlay, on the one hand, a rapid adjustingmovement is possible and, on the other hand, a high force effect canalso be achieved.

The said aim is achieved In such a drive device, therefore, a hydraulicforce intensifier is used, in the pressure space of which a definedvolume of a pressure fluid is enclosed, at least during the adjustingmovement and during the subsequent exertion of a high force, apart fromchanges in volume due to a pressure change. Other hydraulic componentsare not necessary, in principle, for the drive device according to theinvention. According to the invention, the small first hydraulic pistonof the hydraulic force intensifier is connected mechanically to thedrive element axially movable by means of the drive motor designedparticularly as an electric motor. Furthermore, according to theinvention, for the adjusting movement of an element to be driven, thehydraulic unit is movable as a whole, with the result that the speed ofthe large second hydraulic piston coupled mechanically to the element tobe driven is equal to the high speed of the drive element moved axiallyby the electric motor. So that a high force can be exerted, theintermediate part of the hydraulic force intensifier is blocked againstdisplacement in relation to a fixed stand, so that, as a result of afurther movement of the first hydraulic piston over a relatively shortdistance, a high pressure can be built up in the pressure space of theforce intensifier, which generates a high force at the large activesurface of the second hydraulic piston. In this case, only a fraction ofthe force, which corresponds to the active surface of the firsthydraulic piston, has to be supported via the drive element.Particularly with regard to what may be referred to as dual-platemachines, the drive motor and the drive element are preferably arrangedwith respect to the movable part in such a way that, when the high forceis being built up and exerted, the drive element is subjected to tensilestress. Although one drive element is mentioned here, this, of course,also embraces the situation where the drive device has a plurality ofdrive elements interacting in parallel.

So that the hydraulic unit can be moved as a whole, three of itscomponents are coupled to one another in such a way that theintermediate part and the second hydraulic piston follow the driveelement.

Particularly with regard to large plastic injection molding machineswith a high force for keeping the mold shut, a relatively high tear-openforce, which lies in the range of between 5% and 10% of the keeping-shutforce, is also necessary for opening the mold. Since, conversely to whatoccurs during keeping shut, in a dual-plate machine, the drive elementis therefore subjected to compressive load during the tearing-openoperation, it may be the case that the dimensioning of the drive elementmust be governed rather by the necessary tearing-open force than by thenecessary keeping-shut force, in order to prevent a bending of the driveelement. What is achieved here is that, even when a cost-effective driveelement designed for tensile load during keeping shut is used, there isno risk of bending during the tearing-open operation. Hence, both forkeeping shut and for tearing open the mold of a plastic injectionmolding machine, a hydraulic force intensifier is provided for eachdrive element, so that the drive element or drive elements is or aresubjected to only low load. In this case, the piston portion, having thesmall diameter, of a third hydraulic piston designed as a stepped pistonforms the small piston of the hydraulic force intensifier active duringthe tearing-open operation. During the adjusting movement, the thirdhydraulic piston is pressed with the large piston portion, with highforce in the direction of the adjusting movement, against a stop whichis fixed in relation to the housing on which or in which the firsthydraulic piston and the third hydraulic piston are located. The forceis higher than the force which is generated at the first hydraulicpiston by a pressurizing pressure acting upon the first pressure spaceand the active surface of the first hydraulic piston, the pressurizingpressure being selected such that it is above the pressure necessary foraccelerating and moving the second hydraulic cylinder and theintermediate part in the first pressure space. The third hydraulicpiston then acts in the same way as a fixed stop for the first hydraulicpiston. The high pressurizing pressure in the first pressure spacecauses the fluid cushion in the first pressure space to seem like arigid connection between the first hydraulic piston and the housing. Onthe other hand, the third pressure space adjacent to the large pistonportion of the third hydraulic piston can be relieved of pressure, sothat the third hydraulic piston can be displaced in order to tear openthe mold.

A third hydraulic piston may, in principle, be arranged laterally inrelation to the drive element and/or to the first hydraulic piston.Preferably, however, according a feature of the invention, it is inalignment with and upstream of the first hydraulic piston.

If, according to another feature of the invention the first activesurface of the third hydraulic piston is larger than the active surfaceof the first hydraulic piston, the force excess on the third hydraulicpiston is obtained even when the third pressure space and the firstpressure space are acted upon by the same pressure. This pressure may beset by means of a single hydraulic apparatus. Preferably, according tostill another feature of the invention, the first pressure space and thethird pressure space can be connected to the same pressure source, forexample to a hydraulic pump, so as to be acted upon by the samepressure. According to yet another feature of the invention, aswitchable valve is expediently used for the change between pressureaction upon and pressure relief of the third pressure space.

According to another feature of the invention, the fourth hydraulicpiston is adjacent to a pressure space with a boundary wall fixed inrelation to the machine stand. The fourth hydraulic piston can thereforebe firmly connected to or at least be supportable by the secondhydraulic piston or to the machine stand or the mold clamping platefixed in relation to the stand, the corresponding pressure space thenbeing located between the fourth hydraulic piston and the mold clampingplate or the second hydraulic cylinder. The latter version is preferred,since the fluidic connection from the pressure space at the small pistonportion of the third hydraulic piston to the pressure space at thefourth hydraulic piston can then be short, particularly when thepressure space at the second piston portion is likewise located in thesecond hydraulic piston.

According to still another feature of the invention, the fourthhydraulic piston may also be active between the second hydraulic pistonand the intermediate part, in which case said fourth hydraulic pistoncan be fixed with respect to the intermediate part or to the secondhydraulic piston, that is to say is also movable, or is fixed, that isto say permanently immovable, and, in each case with the other part ofthe two parts, intermediate part and hydraulic piston, delimits apressure space which is connected to a pressure space at the secondpiston portion of the third hydraulic piston.

In particular, according to another feature of the invention the fourthhydraulic piston is located in or on the intermediate part or in or onthe second hydraulic piston and is connected to a fifth hydraulic pistonin each case in the other part via a piston rod. The fifth hydraulicpiston serves, for example, in order, after the closing of the mold,when the second hydraulic piston or the movable mold clamping plateconnected to the latter bears against the fixed mold clamping plate, todisplace the intermediate part also somewhat toward the second hydraulicpiston into a locking position, in so far as said intermediate part canbe blocked only at discrete points.

In a design according to yet another feature of the invention, aonce-only setting of the intermediate part and of the second hydraulicpiston in relation to one another when a new molding die is used ispossible with the aid of the fifth hydraulic piston. After setting, thefifth hydraulic piston can remain blocked with respect to the part onwhich it is located, because, for the fourth hydraulic piston, the sixthhydraulic piston implements on the other part a stop which, during thebuild-up of the high keeping-shut force and the associated slightmovement of the second hydraulic piston, can yield, but, for tearingopen the mold, acts as a fixed stop by being acted upon by pressure.According to another feature of the invention, the sixth hydraulicpiston is preferably arranged in alignment with the fourth hydraulicpiston.

To make the fluidic connections between the individual pressure spacesadjacent to the hydraulic pistons, it is beneficial if, according to yetanother feature of the invention, the fourth hydraulic piston or thefourth and the fifth hydraulic piston are located on the same housing asthe first and the third hydraulic piston.

It may be pointed out here, in quite general terms, that the receptionspaces for the hydraulic pistons may be formed in each case directly inthe intermediate part or in the second hydraulic piston or in platesconnected thereto or else separate cylinders having the reception spacesmay be provided, said cylinders being fastened to the intermediate partor to the second hydraulic piston.

BRIEF DESCRIPTION OF THE DRAWINGS

Three exemplary embodiments of a drive device according to theinvention, which are intended in each case for what may be referred toas a dual-plate plastic injection molding machine, are illustrated inthe drawings. The invention, then, is explained in more detail withreference to these drawings in which:

FIG. 1 shows the first exemplary embodiment, in which a fourth hydraulicpiston is guided in a cylindrical receptacle of the second hydraulicpiston and, with the mold closed, can be supported on the fixed moldclamping plate for the purpose of tearing open said mold,

FIG. 2 shows the second exemplary embodiment, in which the fourthhydraulic piston is likewise guided in the second hydraulic piston,moreover is connected via a piston rod to a sixth hydraulic piston andserves with the latter for the releasable coupling of the secondhydraulic piston and of the intermediate part, and

FIG. 3 shows the third exemplary embodiment which is constructed in asimilar way to the second exemplary embodiment, but in which a sixthhydraulic piston guided in the second hydraulic piston forms a movablestop for the fourth hydraulic piston.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the exemplary embodiments shown, two spindle nuts are rotatablymounted axially at a fixed location in a stationary mold clamping plate10, diametrically opposite one another with respect to a center axis 11,via self-aligning roller bearings in a way not illustrated in any moredetail, each of said spindle nuts being capable of being driven inrotation by an electric motor 12 fastened to the mold clamping plate 10.Each spindle nut is in engagement via balls with a threaded portion 13of a rectilinearly movable lifting spindle 14 secured against rotation.A piston rod 15 of a first hydraulic piston 16, which is a small pistonof a hydraulic force intensifier 17, extends from the threaded portion13 of a lifting spindle 14, parallel to the center axis 11, sealed off,through a passage 18 into a cavity 19, having three cylindrical portionsdiffering from one another in their diameters, of a second hydraulicpiston 20 which is the large piston of the hydraulic force intensifier17. Designated here as the second hydraulic piston is a machine partwhich is of essentially plate-shaped design and has a projecting pistonportion 21 (FIGS. 2 and 3), which penetrates into a corresponding pistonreceptacle 23 of an intermediate part 22 of the hydraulic forceintensifier 17, or, set back, a piston receptacle 23 (FIG. 1), intowhich a projecting piston portion 21 of the intermediate part 22penetrates. The piston portion 21 has an active surface 25 which isadjacent to a pressure space 24 and which is substantially larger, forexample thirty times larger, than the active surface 31 of a hydraulicpiston 16. The movable mold clamping plate of the machine is fastened tothe hydraulic piston 20 and is guided along spars in the direction ofthe center axis 11 in a way not illustrated in any more detail.

The passage 18 is followed, in the hydraulic piston 20, first by acavity portion 27, the diameter of which is about three times as largeas the diameter of the piston rod 15. The following cavity portion 28has a larger diameter and is shorter than the cavity portion 27.Finally, the diameter of the last blind-hole-like cavity portion 29 isabout as large as the diameter of the passage 18 and consequently of thepiston rod 15. The hydraulic piston 16 is located in the cavity portion27 and on the piston-rod side is adjacent with an annular active surface30 to an annular pressure space 31. On the side facing away from thepiston rod, the hydraulic piston 16 carries a short tappet 32.

A third hydraulic piston 35 is designed as a stepped piston and islocated with its piston portion 36 of large diameter in the cavityportion 28 and penetrates with a piston portion 37 of small diameterinto the cavity portion 29 in a plunger-like manner. The free spaceupstream of the piston portion 37 is a pressure space which is filledwith pressure medium and may be designated by 33. Located on that sideof the piston portion 36 which faces away from the hydraulic piston 16is an annular pressure space 38 which can be acted upon by systempressure or can be relieved of pressure. The space 39 between the twohydraulic pistons 16 and 35 is permanently relieved of pressure. By theaction of pressure upon the annular active surface 40, which is largerthan the annular active surface 30 on the hydraulic piston 16, from thepressure space 38, the hydraulic piston 35 can be pressed with thepiston portion 36 against the step between the two cavity portions 27and 28, said step constituting an axial stop 41.

The pressure spaces 31 and 38 can be supplied with a fluid pressuremedium which is sucked in from a tank 46 by a hydraulic pump 45 and isconveyed into a pump line 47, to which a pressure limiting valve 48 isconnected in order to set a system pressure. A first valve 50 can bechanged over from a middle working position into two lateral workingpositions. In the middle working position of the valve 50, the pressurespace 31 at the hydraulic piston 18 is fluidically connected to thepressure space 24 at the piston portion 21 of the hydraulic piston 20.In a first lateral working position, the pressure space 31 is connected,throttled, to the pump line 47 and the pressure space 24 is relieved tothe tank. In the other lateral working position, both pressure spaces 24and 31 are relieved to the tank. A second switching valve 51 can assumetwo working positions, the pressure space 38 being connected, throttled,to the pump line 47 in one working position and being relieved to thetank in the other working position.

In all three exemplary embodiments shown, the intermediate part 22 ofthe hydraulic force intensifier 17 can be firmly connected to thehydraulic piston 20 via a releasable coupling device, so that, duringthe closing of the mold, that is to say during the adjusting movement,the hydraulic piston 20 and the intermediate part 22 can be moved as aunit. After the closing of the mold, the coupling between the hydraulicpiston 20 and the intermediate part 22 is released and the intermediatepart is retained in relation to the machine stand. In principle, theblocking device between the intermediate part and the machine stand orthe mold clamping plate fixed in relation to the latter may be designedin such a way that, within a defined zone, blocking at infiniteintervals is possible at any desired point. With regard to the exemplaryembodiment according to FIG. 1, such a possibility may be assumed to beafforded.

In the exemplary embodiment according to FIG. 1, the hydraulic piston 20possesses, distributed at uniform intervals about the center axis 11, aplurality of blind-hole-like cylindrical receptacles 54 which are opentoward the fixed mold clamping plate 10. In each receptacle 54, aplunger piston 55 is guided, as the fourth hydraulic piston of theexemplary embodiment according to FIG. 1, is held in the receptacle 54by a spring 56, projects from the receptacle and, with the mold closed,can be supported on the fixed mold clamping plate 10. The pressure space57 in the receptacle 54 upstream of the plunger piston 55 is connectedto the pressure space 33 upstream of the piston portion 37 of thehydraulic piston 35.

In the exemplary embodiments according to FIGS. 2 and 3, theintermediate part 22 can be interlocked, with the aid of toothed lockingrods 59 fastened to the fixed mold clamping plate and extending in thedirection of the center axis 11, together with the fixed mold clampingplate 10 and consequently with the machine stand at discrete pointsspaced slightly apart from one another. The hydraulic piston 20 receivesa fourth hydraulic piston 65 in each of a plurality of cylindricalcavities 64 distributed uniformly about the center axis 11. Theintermediate part 22 likewise receives a fifth hydraulic piston 67 ineach case in each of a plurality of cylindrical cavities 66 which are inalignment with the cavities 64 in the hydraulic piston 20. The twohydraulic pistons 66 and 67 lying in alignment with one another arefirmly connected to one another via a piston rod 68. The pressure space69, on the side facing away from the piston rod, at the hydraulic piston65 is either connected, throttled, to the pump line 47 or relieved tothe tank via a switching valve 70 having two working positions. Thecircular-cylindrical active surfaces 71, on the side facing away fromthe piston rod, of the two hydraulic pistons 65 and 67 are of equalsize. The pressure space 57, on the piston-rod side, at the hydraulicpiston 65, said pressure space corresponding to the identicallydesignated pressure space from FIG. 1, is connected permanently to thepressure space 33 at the piston portion 37 of the stepped piston 35.

In the version according to FIG. 2, the hydraulic piston 65 can beardirectly against the hydraulic piston 20 on the piston-rod side. Bycontrast, in the exemplary embodiment according to FIG. 3, the stop onthe side of the piston rod 68 for the hydraulic piston 65 is formed by asixth hydraulic piston 75 and can be switched to active and inactive.The hydraulic piston 75 has a larger outside diameter than the hydraulicpistons 65 and 67 and is located in a cavity 76 of larger diameter whichis adjacent to the cavity 64 on the same side as the piston rod 68. Thepiston rod 68 passes, sealed off, through a central orifice of thehydraulic piston 75. On that side of the hydraulic piston 75 which facesaway from the hydraulic piston 65, the pressure space 77 is eitherconnected, throttled, to the pump line 47 or relieved to the tank via aswitching valve 78 having two working positions. When the pressure space77 and consequently an annular active surface 79 at the hydraulic piston75 are acted upon by system pressure, the hydraulic piston 75 bearsagainst the step 80 between the two cavities 64 and 76 and acts in thesame way as a fixed boundary of the cavity 64. System pressureprevailing in the pressure space 69 cannot lift off the hydraulic piston75 from the step, since the active surface 79 at the hydraulic piston 75is larger than the active surface 71 at the hydraulic piston 65. Thehydraulic piston 65 bears against the hydraulic piston 75 via a collarhaving an increased diameter in relation to the diameter of the pistonrod 68. The annular pressure space between the two hydraulic pistons 65and 75 corresponds to the pressure space 57 of the exemplary embodimentaccording to FIG. 2 and is connected to the pressure space 33 at thepiston portion 37 of the hydraulic piston 35. During the relief of thepressure space 77, the hydraulic piston 65 can lift off the hydraulicpiston 75 from the step 80, the volume of the pressure space 57 betweenthe two hydraulic pistons increasing. When the hydraulic piston 75approaches the step, the volume decreases. So that the change in volumecan be compensated, the two pressure spaces 33 and 57 are connected tothe tank in a second of two working positions of a switching valve 85.In the first working position, the two pressure spaces are shut off,free of leakage.

In the exemplary embodiment according to FIG. 3, after a new die hasbeen mounted, when the pressure spaces 69 and 77 are acted upon bysystem pressure with the aid of the hydraulic piston 67, at thehydraulic piston 20 the intermediate part 22 is brought into a positionlying as near as possible to the hydraulic piston 20, such that, withthe mold closed, said intermediate part assumes with respect to thelocking rods 59 a position such that it can be locked. For this purpose,the pressure spaces on both sides of the hydraulic piston 67 can beconnected to the pressure source and to a tank via a throttling controlvalve not illustrated in any more detail. The pressure which isestablished in one or the other pressure space of the hydraulic piston67 during the setting operation is substantially lower than the systempressure. After this setting, the two pressure spaces are shut off, freeof leakage. As long as the same die is used, in principle, no furthersetting is necessary.

Assuming an open mold, then, the mold is to be closed. The valve 50assumes the working position in which the pressure space 24 is relievedto the tank and the pressure space 31 is connected to the pump line 47.The pressure space 69 is also connected via the valve 70 and thepressure space 77 via the valve 78 to the pump line 47. System pressureprevails in the pressure spaces. The pressure spaces 33 and 57 arerelieved to the tank via the valve 85. If, then, the lifting spindle ismoved in the direction of the fixed mold clamping plate 10, thehydraulic piston 20 is taken up via the hydraulic piston 16 and via thepressurized, that is to say compressed pressure-medium cushion locatedin the pressure space 31, without the pressure medium in this case beingcompressed any further. There is a virtually rigid connection betweenthe lifting spindle 14 and the hydraulic piston 20. The intermediatepart 22 is taken up, likewise in a virtually rigid manner, by thehydraulic piston 20 via the pressure-medium cushion in the pressurespace 77, the two hydraulic pistons 75 and 65, the piston rod 68, thehydraulic piston 67 and the pressure-medium cushion in one pressurespace of the latter.

After the closing of the mold, the intermediate part 22 is locked withrespect to the machine stand. The two valves 70 and 78 change over, sothat the two pressure spaces 69 and 77 are relieved to the tank. Thevalve 50 is brought into the working position in which the two pressurespaces 24 and 31 are connected to one another. The pressure space 38remains connected to the pump line 47 via the valve 51, so that thehydraulic piston 35 is held reliably against the stop 41. If, then, thehydraulic piston 16 is moved further on in the direction of the moldclamping plate 10, a high keeping-shut pressure lying above the systempressure can build up in the pressure spaces 24 and 31 connected to oneanother and generates a very high keeping-shut force at the large activesurface 25 of the hydraulic piston 20. In the event of a slight movementof the hydraulic piston 20 which still takes place in this case, thehydraulic piston 75 upstream of the hydraulic piston 65 can readily betaken up, since the pressure space 77 is relieved of pressure.

After the injection of the plastic into the mold, after a possibledwell-pressure phase and after a solidification time, the liftingspindle 14 is moved in the direction away from the fixed mold clampingplate 10 and the pressure medium in the pressure spaces 24 and 31 isthereby expanded. After expanding, the hydraulic piston 16 bears withthe tappet 32 against the hydraulic piston 36. The valve 50 is broughtinto the working position in which the two pressure spaces 24 and 31 arerelieved to the tank. The valve 51 changes over, so that the pressurespace 38 is relieved to the tank. The valve 78 changes over, so that thepressure space 77 is acted upon by the system pressure. The valve 85changes over in order to shut off the two pressure spaces 33 and 57relative to the tank. As a result of the movement of the lifting spindle14, then, the hydraulic piston 35 is moved by the latter, via thehydraulic piston 16 and the tappet 32, with the effect of a reduction inthe pressure space 33, so that pressure medium is displaced out of thispressure space into the pressure space 57. A pressure builds up there,which generates at the hydraulic piston 75 a force which reduces thebearing force of said hydraulic piston against the step 80 of thehydraulic piston 20. The reaction force is absorbed via the hydraulicpistons 65 and 67 by the intermediate part 22 and consequently by themachine stand. Finally, the bearing force of the hydraulic piston 75 isreduced to an extent such that the excess force generated by the systempressure prevailing in the pressure space 77 is sufficient to separatethe mold halves from one another. The progress of this tearing open ofthe mold may in this case be controlled via the traveling speed of thelifting spindle 14. The pressure space 69 is in this case reduced due tothe relative movement between the hydraulic piston 20 and the hydraulicpiston 65.

After the tearing-open operation, the locking of the intermediate plate22 is released. The valve 85 switches and connects the two pressurespaces 33 and 57 to the tank. Moreover, the two valves 51 and 70 changeover, so that pressure medium can flow, throttled, to the pressurespaces 38 and 69 from the pump line 47, as indicated in the respectivecircuit diagram by the nozzle. The hydraulic piston 20 and theintermediate part 22 move relative to one another and to the liftingspindle in such a way that they assume the positions, shown in FIG. 3,in relation to one another and to the lifting spindle.

The valve 50 is then brought into the working position in which itconnects the pressure space 31 to the pump line 47. The pressure space31 is acted upon by system pressure, so that the hydraulic piston 20 andthe intermediate part 22 continue to follow exactly the movement of thelifting spindle 14 in the opening direction into the opening position.

The exemplary embodiment according to FIG. 2 lacks, as compared with theexemplary embodiment according to FIG. 3, the stop, to be made activeand inactive, for the hydraulic piston 65. During the closing of themold, the valves 50, 51 and 70 assume the same positions as in theexemplary embodiment according to FIG. 3 in the same movement phase. Thehydraulic piston 65 bears against the hydraulic piston 20 on thepiston-rod side, and the hydraulic piston 67 is blocked with respect tothe intermediate part 22.

When the mold is closed, the intermediate part 22 is positioned at thehydraulic piston 67, by the supply of pressure medium into one pressurespace and by the discharge of pressure medium out of the other pressurespace, in such a way that said intermediate part can be interlocked withthe locking rods 59. During positioning, the pressure space 24 is stillconnected to the tank via the valve 50, so that a change in volume canbe compensated. After the locking of the intermediate part 22, thehydraulic piston 67 is switched so as to be freely movable by means ofthe connection of the two pressure spaces adjacent to it to the tank.The valve 50 is brought into the position in which the pressure spaces24 and 31 are connected to one another. As a result of a furthermovement of the lifting spindle 14 and consequently of the hydraulicpiston 16 in the closing direction, a high pressure builds up in thepressure spaces 31 and 24 and generates a high keeping-shut force at thelarge active surface 25. In the event of a slight movement of thehydraulic piston 20 which still takes place in this case, the hydraulicpiston 65 can readily be taken up, since the hydraulic piston 67 isswitched free.

After the injection of the plastic into the mold, after a possibledwell-pressure phase and after a solidification time, the liftingspindle 14 is moved in the direction away from the fixed mold clampingplate 10 and the pressure medium in the pressure spaces 24 and 31 isthereby expanded. After expansion, the hydraulic piston 16 bears withthe tappet 32 against the hydraulic piston 35. The valve 50 is broughtinto the working position in which the two pressure spaces 24 and 31 arerelieved to the tank. The valve 51 changes over, so that the pressurespace 38 is relieved to the tank. The hydraulic piston 67 is blockedhydraulically with respect to the still locked intermediate part 22. Asa result of the movement of the lifting spindle 14, then, as in theexemplary embodiment according to FIG. 3, the hydraulic piston 35 ismoved by the latter, via the hydraulic piston 16 and the tappet 32, withthe effect of a reduction of the pressure space 33, so that pressuremedium is displaced out of this pressure space into the pressure space57. A pressure builds up there, which acts directly upon the hydraulicpiston 20 at a surface corresponding to the annular surface of thehydraulic piston 65 and which generates a tearing-open force. Thereaction force is absorbed via the hydraulic pistons 65 and 67 by theintermediate part 22 and consequently by the machine stand.

After the tearing-open operation, the locking of the intermediate plate22 is released. The two valves 51 and 70 change over, so that pressuremedium can flow, throttled, to the pressure spaces 38 and 69 from thepump line 47. The hydraulic piston 20 and the intermediate part 22 moverelative to one another and to the lifting spindle in such a way thatthey assume the positions, shown in FIG. 2, in relation to one anotherand to the lifting spindle.

The valve 50 is then brought into the working position in which itconnects the pressure space 31 to the pump line 47. The pressure space31 is acted upon by system pressure, so that the hydraulic piston 20 andthe intermediate part 22 continue to follow exactly the movement of thelifting spindle 14 in the opening direction into the opening position.

In the exemplary embodiment according to FIG. 1, during the closing ofthe mold, the valves 50 and 51 assume the same positions as in theexemplary embodiment according to FIG. 3 in the same movement phase. Thepressure spaces 31 and 38 are therefore connected to the pump line 47and are acted upon by system pressure.

When the mold is closed, the intermediate part 22 is blocked in relationto the machine stand. The valve 50 is thereafter brought into theposition in which the pressure spaces 24 and 31 are connected to oneanother. As a result of the further movement of the lifting spindle 14and consequently of the hydraulic piston 16 in the closing direction, ahigh pressure builds up in the pressure spaces 31 and 24 and generates ahigh keeping-shut force at the large active surface 25.

After the injection of the plastic into the mold, after a possibledwell-pressure phase and after a solidification time, the liftingspindle 14 is moved in the direction away from the fixed mold clampingplate 10 and the pressure medium in the pressure spaces 24 and 31 isthereby expanded. After expansion, the hydraulic piston 16 bears withthe tappet 32 against the hydraulic piston 35. The valve 50 is broughtinto the working position in which the two pressure spaces 24 and 31 arerelieved to the tank. The valve 51 changes over, so that the pressurespace 38 is relieved to the tank. As a result of the movement of thelifting spindle 14, then, as in the exemplary embodiments according toFIGS. 2 and 3, the hydraulic piston 35 is moved by the latter, via thehydraulic piston 16 and the tappet 32, with the effect of a reduction ofthe pressure space 33, so that pressure medium is displaced out of thispressure space into the pressure space 57. A pressure builds up there,which acts directly upon the hydraulic piston 20 at a surfacecorresponding to the active surface of the hydraulic piston 55 supportedon the stationary mold clamping plate 10 and which generates atearing-open force.

After the tearing-open operation, the blocking of the intermediate plate22 is released. The valves 50 and 51 change over, so that pressuremedium can flow, throttled, to the pressure spaces 31 and 38 from thepump line 47. The hydraulic piston 20 and the intermediate part 22 movein relation to the lifting spindle in such a way that they assume thepositions in relation to the lifting spindle which are shown in FIG. 1.The hydraulic piston 20 and the intermediate part then exactly followthe movement of the lifting spindle 14 in the opening direction into theopening position.

1. A drive device, in particular for driving a movable part of a closingunit or of an injection unit of a plastic injection molding machineduring an adjusting movement and for subsequent build-up and exertion ofa high force, comprising a drive element (14) movable axially by meansof a drive motor (12), in particular by means of an electric motor, ahydraulic unit (17) movable as a result of movement of the drive element(14) in same direction as the latter, wherein the hydraulic unit (17) isa force intensifier with a first and a second of two hydraulic pistons(16, 20) movable in relation to one another and differing from oneanother in the size of their active surfaces (30, 25) and with anintermediate part (22), wherein the first hydraulic piston (16) havingthe smaller active surface (30) is connected mechanically to the driveelement (14), wherein for the adjusting movement, the hydraulic unit(17) is movable as a whole, wherein for exerting a high force by meansof the second hydraulic piston (20) having the larger active surface(25), the intermediate part (22) can be blocked against displacement inrelation to a fixed stand (10), and wherein the first hydraulic piston(16) being adjacent with its active surface (30) to a first pressurespace (31) in or on a housing formed by the second hydraulic piston (20)or by the intermediate part (22), said pressure space being fluidicallyconnectable to a second pressure space (24), which is adjacent to thesecond hydraulic piston (20), in one position of a valve (50), via thelatter, and to a pressure source (45) in another position of the valve(50), wherein a third hydraulic piston (35) designed as a stepped pistonis present with a first active surface (40) at a first piston portion(36) and with a second active surface at a second piston portion (37),wherein the third hydraulic piston (35), by action of pressure upon athird pressure space (38) adjacent to its first active surface (40), ispressable in direction of adjusting movement of the first hydraulicpiston (16) against a stop (41) fixed in relation to the housing (20),with a force which is higher than the force exerted on the housing (20)in same direction by the pressure in the first pressure space (31),wherein when the third pressure space (38) is relieved of pressure, thethird hydraulic piston (35) is movable away from the stop (41) indirection opposite to the adjusting movement of the first hydraulicpiston (16), and wherein the second piston portion (37) of the thirdhydraulic piston (35) forms, with a fourth hydraulic piston (55, 65)having an active surface larger than the second active surface of thethird hydraulic piston (35), a hydraulic force intensifier for actingupon the second hydraulic piston (20) opposite to the adjustingmovement.
 2. The drive device as claimed in claim 1, wherein the thirdhydraulic piston (35) is arranged in alignment with the first hydraulicpiston (16).
 3. The drive device as claimed in claim 1, wherein thefirst active surface (40) of the third hydraulic piston (35) is largerthan the active surface (30) of the first hydraulic piston (16), andwherein the third pressure space (38) and the first pressure space (31)are actable upon by same pressure.
 4. The drive device as claimed inclaim 3, wherein the first pressure space (31) and the third pressurespace (38) are connectable to the same pressure source (45) in order tobe acted upon by the same pressure.
 5. The drive device as claimed inclaim 4, wherein the third pressure space (38) via a switchable valve(51) is connectable to the pressure source (45) and relievable ofpressure.
 6. The drive device as claimed in claim 1, wherein the fourthhydraulic piston (55) is adjacent, with a boundary wall fixed inrelation to the machine stand (10), to a pressure space (57).
 7. Thedrive device as claimed in claim 1, wherein the fourth hydraulic piston(65) is fixable or is fixed with respect to the intermediate part (22)or to the second hydraulic piston and, in each case with the other part(20) of the two parts, intermediate part and hydraulic piston, delimitsa pressure space (57) which is connected to a pressure space (33) at thesecond piston portion (37) of the third hydraulic piston (35).
 8. Thedrive device as claimed in claim 7, wherein the fourth hydraulic piston(65) is located in or at the intermediate part or the second hydraulicpiston (20) and is connected to a fifth hydraulic piston (67) in eachcase in the other part (22) via a piston rod (68).
 9. The drive deviceas claimed in claim 8, wherein a sixth hydraulic piston (75), by theaction of pressure upon a pressure space (77) adjacent to an activesurface of the latter, is pressable against a stop (80) which is fixedin relation to part (20) in which the fourth hydraulic piston (65) islocated, wherein the fourth hydraulic piston (65) is pressable, with alower force than that with which the sixth hydraulic piston (75) ispressable against the stop (80), against the sixth hydraulic piston (75)with the effect of lifting off the sixth hydraulic piston (75) from thestop (80), and wherein, when the sixth hydraulic piston (75) is relievedof pressure, the latter is liftable off from the stop (80) by the fourthhydraulic piston (65).
 10. The drive device as claimed in claim 9,wherein the sixth hydraulic piston (75) is actable upon, in thedirection of the stop (80), and the fourth hydraulic piston (65) isactable upon, with the effect of lifting off the sixth hydraulic piston(75) from the stop (80), by the same pressure at active surfaces (79,71) of unequal size.
 11. The drive device as claimed in claim 9, whereinthe sixth hydraulic piston (75) is arranged in alignment with the fourthhydraulic piston (65) and has a central perforation for a piston rod(68) connected to the fourth hydraulic piston (65).
 12. The drive deviceas claimed in claim 10, wherein the sixth hydraulic piston (75) isarranged in alignment with the fourth hydraulic piston (65) and has acentral perforation for a piston rod (68) connected to the fourthhydraulic piston (65).
 13. The drive device as claimed in claim 1,wherein the fourth hydraulic piston (65) is arranged in or on the samehousing (20) as the first hydraulic piston (16) and the third hydraulicpiston (35).
 14. The drive device as claimed in claim 9, wherein thefourth hydraulic piston (65) and the sixth hydraulic piston (75) arearranged in or on the same housing (20) as the first hydraulic piston(16) and the third hydraulic piston (35).